The family of former US President Barack Obama have paid tribute to "our best friend", after their beloved pet dog Bo died on Saturday. Bo, Michelle Obama wrote in a social media post, had been a "constant, comforting presence" since his arrival in the White House in 2009. The black and white Portuguese water dog was a gift for their daughters as they settled into their new home. "We had no idea how much he would mean to all of us," Mrs Obama wrote. "He was exactly what we needed and more than we ever expected," Barack Obama wrote in his own post, noting how Bo had been "happy to see us on our good days, our bad days, and every day in between". For the last 100 years, with the exception of Donald Trump, US presidents have had pets. Current President Joe Biden has two dogs, although Major - the younger of the two - has got in trouble for biting. During his tenure as "First Dog", Bo became so popular that Mrs Obama was sent a memo at the beginning of each month so she could approve official appearances. He was joined by fellow Portuguese water dog Sunny in 2013. "He tolerated all the fuss that came with being in the White House, had a big bark but no bite, loved to jump in the pool in the summer, was unflappable with children, lived for scraps around the dinner table, and had great hair," Mr Obama said in his post. Mrs Obama said the former First Dog had later helped the couple as they adjusted to "life as empty nesters" when their daughters Malia and Sasha left home for university. But, she added, "no one was happier than Bo" when everyone returned home during the pandemic. Bo died "after a battle with cancer", Mrs Obama said in her post, signed from the whole family.